131 Java Testing Unit Testing

This is a comprehensive testing modernizer for Java projects. It walks you through migrating from JUnit 4 to JUnit 5, switching to AssertJ's fluent assertions, and applying proper test structure with Given-When-Then. What's useful here is the safety-first approach: it forces you to compile before making changes and verify afterward, which prevents breaking your build mid-refactor. The skill covers the full testing stack including Mockito mocking, parameterized tests, and boundary condition verification using RIGHT-BICEP and CORRECT principles. It's built for teams trying to eliminate common anti-patterns like reflection-based tests and shared mutable state while adopting modern practices like JSpecify null-safety annotations.